The present invention relates generally to methods for cleaning dental and medical instruments. In particular, the invention is according to one aspect directed to a novel process of carrying out the cleaning of dental and surgical instruments to optimize both corrosion protection and cleaning efficiency.
According to another aspect, the present invention is directed to novel detergent-anti corrosion compositions for medical and surgical instruments which are particularly adapted for use in the cleaning process of the present invention.
Despite being fabricated from stainless steel, dental and medical instruments are subject to corrosion during the maintenance cycle (washing, disinfection, sterilization). Dental instruments are typically more susceptible to corrosion, owing to their higher carbon content. In order to achieve desired instrument characteristics such as surface hardness and durability, instrument manufacturers often resort to manufacturing processes such as heat treatment which also have the undesirable effect of compromising the resistance of the instruments to corrosion. In order to reduce the magnitude and rate of the process of corrosion, or even to prevent it from taking place altogether, some active corrosion protection steps have to be taken.
It has been known that in some cases, even just prolonged exposure to fresh water would start corrosion on the instrument surface. Some detergents developed for cleaning of medical instruments contain rust inhibitors. The action of these inhibitors is limited to the washing stage of the cleaning cycle, the only stage during which the detergent is used, conventionally. This typically excludes all rinsing stages and the final air-drying stage of the cleaning cycle. To cover these stages as well, different sets of chemicals are often used. These chemicals are known as rinse aids with rust inhibitors. A rinse aid serves the dual purpose of (i) changing rinse water properties in order to aid in the drying of the instruments, and (ii) improving protection against rust. Surgical milk products can also be used to protect the instruments' surface from corrosion after a rinse stage.
Such processes create the need for a number of different chemicals to be used during the wash cycle. The cost of individual chemicals, handling and chemical dispensing systems makes the cleaning process expensive and complex.
A typical cycle for cleaning medical instruments consists of a number of consecutive stages: pre-wash, wash, rinses (usually two) and drying. The pre-wash stage is used to dissolve blood on the instruments and it is run with cold water so as to prevent blood coagulation. The wash part of the cycle is run with hot/warm water and a detergent. Wash time, water temperature and detergent are matched according to requirements. A number of rinses are used to remove soil dissolved in the wash stage as well as the remaining detergent.
A number of detergents enhanced with rust inhibitors have been developed specifically for use in ultrasonic washers, where rinsing of the instruments is not recommended in order to maintain the presence of the detergent on the instruments' surface. An example is afforded by the Ultrasonic Solution made by Health Sonics Corporation. The rust inhibitors remain on the surface of the instruments after the cleaning cycle is finished. This rust protection has a time-limited action and will evaporate from the surface or get burned off during the usual high-temperature sterilization process, so that essentially no residuals are left on the surface of the instrument when it is next used on a patient.
Unfortunately, by avoiding the rinse stage in order to obtain the maximum protective effect of such rust inhibitors, the cleanliness of the instruments can be compromised. The very purpose of a rinse stage is to rinse away dirt loosened and dissolved in the wash stage, and to flush it out together with used detergent.